A communication device performing microwave communication or millimeter wave communication includes a band pass filter that passes only high-frequency signals of a desired frequency band and attenuates signals of unwanted frequency bands. In recent years, in designing a communication system, there has been an increasing demand for a band pass filter included in the communication device whose center frequency of a passband is externally variable.
Related art such as Patent Literatures 1 to 3 each disclose the technique of structuring a band pass filter using a TE01δ-mode dielectric resonator (DR), and externally adjusting the resonance frequency of the dielectric resonator. Specifically, according to the technique disclosed in Patent Literatures 1 and 2, a conductive plate is disposed between a dielectric resonator and a housing covering the dielectric resonator. The resonance frequency is adjusted by varying the interval between the conductive plate and the dielectric resonator. Further, according to the technique disclosed in Patent Literature 3, an adjustment screw is inserted into an adjustment hole provided at the upper surface of a housing covering the dielectric resonator, in which the adjustment hole is positioned above the dielectric resonator. The resonance frequency is adjusted by varying the insertion amount of the adjustment screw.